Method- of preparing unsaturated



Patented Jan. 26, 1954 UNITED STATES PATENT OFFICE METHOD OF PREPARING UNSATURATED vETHERS No Drawing. Application June 15,1951, Serial No. 233,117

6 Claims. Cl. 260-614) The present invention relates to the production of alkyl alkylene ethers and deals more particularly with the method or preparing such ethers from acetals.

The production of alkyl alkylene others by cat- 5 alytic, vapor phase thermal dissociation of vacetals of aliphatic aldehydes or ketones is well known. I have found, however, that the percentage conversion obtained according to the prior processes, as well as the engineering problems incident thereto, render the prior vapor phase processes commercially unfavorable. According to Claisen (Berichte, 31 1021) the liquid phase conversion of acetals into alkyl alkylene ethers may be r effected by prolonged heating with phosphorus pentoxide in the presence of quinoline. This liquid phase method requires the use of excessive quantities of phosphorus pentoxide, the reaction proceeding, not by thermal dissociation, but by a chemical de-alcoholating reaction wherein there are formed as Icy-products esters of phosphoric acid and the cleaved alcohol.

Now I have found that the liquid phase conversion of certain acetals to alhyl alkylene ethers is effected eificiently and smoothly by contacting the acetals with a hot solution of an aromatic or alkylaromatio sulfonic acid of from 6 to 18 carbon atoms in an inert high boiling solvent. Solvents boiling at a temperature of at least 175 C. are preferred.

Conversion of the acetals to the alkyl alkylene ethers proceeds substantially according to the scheme:

in which R and R are selected from the class consisting of hydrogen and alkyl radicals of from 1 to '7 carbon atoms, Y is selected from the class consisting of hydrogen and alkyl radicals of from 40 1 to 8 carbon atoms, Z is an alkyl radical of from 1 to 2 carbon atoms, and the total number of carbon atoms in the acetal molecule is from 4 to .21 and the total number of carbon atoms in the ether molecule is from 3 to 26. Generally there is obtained a mixture of the cis and trans forms of the alkenyl alkyl ether:

and

RCH:C.OZ

In some instances, the mixture of isomers may be resolved by fractional distillation; however, more frequently, the boiling points of the individual isomers are within too narrow a range to permit a practical fractionation.

Acetals which may be used in the present process are e. g., the dimethyl and the diethyl acetals of such saturated aliphatic aldehydes as acetaldehyde, butyraldehyde, isobutyraldehyde, n-valeraldehyde, n-hexaldehyde or n-octaldehyde and such saturated, aliphatic ketones as acetone, diisopropyl ketcne, methyl ethyl ketone, di-n-butyl ketone. di-n-octyl ketone, etc.

Alkyl alkylene ethers obtainable by the present process include, e. g., methyl vinyl ether, ethyl propenyl ether, ethyl isopropenyl ether, methyl 1- butenyl ether, methyl i-hexenyl ether, ethyl 4- hept-3-eny1 ether, methyl l-octenyl ether, etc.

The acid may be present in the solution in only catalytic quantities with respect to the acetal, e., in quantities of from 1% to 10% based on the acetal. Acids which may be employed to effect the catalytic, liquid phase conversion of acetals to alkyl alkylene ethers according to the present process are aromatic sulfonic acids such as benzene sulfonic acid, the naphthalenesulfonic acids, and the biphenylsulfonic acids; alkylaromatic sulfonic acids such as -toluenesulfonic acid, 4- butylbenzenesulfonic acid, Z-(Z-ethylhexyDbenzene sulfonic acid, dodecylbenzenesulfonic acid, .etc.

Solvents employed for the reaction are generally hydrocarbons or chlorine-substituted hydrocarbons. Examples of useful solvents are isononylbenzene, dodecylbenzene, biphenyl, naphthalene, kerosene, 2-chloronaphthalene, -chlorobiphenyl, technical mixtures of chlorinated products obtained by elemental chlorination of herosene, benzene, naphthalene, biphenyl, polyphenyls, etc. Preferred solvents are highly chlorin- .ated aromatic hydrocarbons such as perchlorobenzene and the polychlorinated polyphenyls known to the trade as Aroclors.

The temperature of the sulfonic acid solution with which the acetals are contacted may be from, vsay, C. upto the boiling point of the solvent. When operating batchwise, the acetal is simply mixed with the solution of acid, and the resulting mixture maintained at a temperature of from, say, 140 C. to 250 C. until conversion of the acetal to the alkylene ether is substantially completed. Preferably, however, I employ a continuous process, whereby the acetal is gradually introduced, e. -g., dropwise, into the hot, acid solution while removing the reaction products from the reaction zone. Therefore, when operating continuously the boiling point of the diluent is necessarily greater than the boiling point of the product mixture which is being distilled. Generally, this distillate consists of a mixture of the alkylene ether and by-product alcohol, from which the ether may be readily separated by known methods, e. g., by fractional distillation, solvent extraction, etc.

The invention is further illustrated, but not limited, by the following examples.

Emample 1 A solution of 3 g. of 4-toluenesulfonic acid in 200 g. of a polychlorinated polyphenyl known to the trade as Aroclor 1242 was placed into a 500 ml. 3-neck flask equipped with stirrer, dropping funnel and thermometer and attached to a 4 Vigreux column. The solution was heated to 180 C., and to the hot solution, while stirring, there was added dropwise 340 g. of diethyl butyral during 2.5 hours. During the addition, the pot temperature was from 180 C. to 240 C., and the take-off was adjusted so that the product having a boiling point of about 80 C. was continuously distilled into 5 g. of a-picoline. Fractionation of this product gave an azeotrope of ethanol and l-butenyl ethyl ether, 13. P. '72'74 C. Addition of hexane to the azeotrope and subsequent distillation gave 55 g. of l-butenyl ethyl ether, B. P. 91-4 C., N 1.4045 and 100 g. of l-butenyl ethyl ether, B. P. 946 C., N 1.4039.

Example 2 Employing the apparatus described in Example 1, 1018 g. of dimethyl butyral were added dropwise, at a temperature of from 180 C. to 250 C. and during a period of 4.5 hours to a solution of 3 g. of 4-toluenesulfonic acid in 300 g. of a polychlorinated polyphenyl known to the trade as Aroclor 1254. Product distilling over at about 60 C. was continuously removed. The total distillate was washed with 200 m1. of 1% aqueous sodium hydroxide, the whole was allowed to stratify, and the upper organic layer separated. Dehydration of this organic layer was effected by distilling with a Dean and Stark water-trap; and subsequent distillation of the dehydrated material yielded 600 g. of a mixture of cisand transl-butenyl methyl ether, B. P. '72-'75 C. which was shown by infra-red analysis to consist chiefiy of the cis-isomer, and 40 g. of a fraction, 13. P. '75 C., a mixture of the stereoisomeric l-butenyl methyl ethers containing a lower proportion of the cis-isomer than the 72-'75 C. fraction.

The present invention, it will be noted, provides an easy and eflicient method for the preparation of alkyl alkenyl ethers from acetals. In contrast to known liquid phase processes, there are employed no excessive quantities of de-alcoholating reagents. lhe aromatic or alkylaromatic sulfonic acids serve as catalysts, i. e., they are not consumed in the reaction, and they are employed in only catalytic quantities. The solvent employed serves merely as a heating medium and likewise undergoes no deterioration during the reaction.

While the above examples show only the use of the chlorinated polyphenyls as solvents, these solvents being employed only in order to assure heat-stability under the wide variety of conditions which are often encountered in obtaining experimental data, high-boiling hydrocarbons, generally, or chlorine substitution products thereof may be used. Also instead of employing 4- toluenesulfonic acid as catalyst, there may be used aromatic or alkylaromatic sulfonic acids, generally, e. g., 4-tert-butylsulfonic acid, benzenedisulfonic acid, p-naphthalenesulfonic acid, etc.

Although the invention has been illustrated with reference to acetals of butyraldehyde, it is not to be regarded as limited to the specific acetals used, but is applicable to acetals of other aldehydes or to acetals of ketones, as herein disclosed.

What I claim is:

1. The method of producing an ether having the formula R.( 3:C(Y)(0Z) in which R and R are selected from the class consisting of hydrogen and alkyl radicals of from 1 to '7 carbon atoms, Y is selected from the class consisting of hydrogen and alkyl radicals of from 1 to 8 carbon atoms and Z is an alkyl radical of from 1 to 2 carbon atoms, and the total number of carbon atoms in the ether molecule is from 3 to 20, which comprises contacting an acetal having the general formula in which R and R are selected from the class consisting of hydrogen and alkyl radicals of from 1 to 7 carbon atoms, Y is selected from the class consisting of hydrogen and alkyl radicals of from 1 to 8 carbon atoms and Z is an alkyl radical of from 1 to 2 carbon atoms, with a liquid, maintained at a temperature of from C. to 250 C. and comprising a solution of a sulfonic acid selected from the class consisting of aromatic and alkylaromatic sulfonic acids of from 6 to 18 carbon atoms in a solvent selected from the class of hydrocarbons and chlorine-substituted hydrocarbons having a boiling point of at least C.

2. The process of preparing l-butenyl methyl ether which comprises contacting dimethyl butyral with a solution of 4-toluenesulfonic acid in a mixture of polychlorinated polyphenyl compounds at a temperature of from 140 C. to 250 C.

3. The process of preparing l-butenyl ethyl ether which comprises contacting diethyl butyral with a solution of 4-toluenesulfonic acid in a mixture of polychlorinated polyphenyl compounds at a temperature of from 140 C. to 250 C.

4. The process defined in claim 1, further characterized in that the acetal is continuously introduced into said solution while the ether produced is continuously distilled from said solution.

5. The process defined in claim 2, further characterized in that said butyral is continuously introduced into said solution while the l-butenyl methyl ether formed is continuously distilled from said solution.

6. The process defined in claim 3, further characterized in that the butyral is continuously introduced into said solution while the l-butenyl ethyl ether fomred is continuously distilled from said solution.

RAYMOND I. LONGLEY, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,189,529 Carothers et a1 Feb. 6, 1940 Bramwyche et a1. Sept. 20, 1949 

1. THE METHOD OF PRODUCING AN ETHER HAVING THE FORMULA 